The acquisition of force data, often in the form of pressure measurement, is important for numerous applications. The automotive and medical industries utilize force sensor and pressure measuring systems to, for example, monitor and control a variety of substances and equipment. For example, in the medical industry precise and accurate information regarding the infusion into a patient of intravenous ("I.V.") solutions through I.V. tubing and of nutrients through tubing and a feeding pump can be critical to the patient's well being.
To properly control and monitor the infusion flow rate of I.V. solutions, force sensors may be positioned to measure the I.V. solution pressure. FIG. 1, labeled prior art, illustrates in cross-section an I.V. tube 102 compressively engaged between a solid surface 104 and a force sensor 106. One approach to measuring I.V. solution pressure within tube 102 involves capturing and partially compressing I.V. tube 102 between force sensor 106 and solid surface 104. The force sensor 106 detects a force on the tubal wall 108 corresponding to varying I.V. solution pressure exerted within tube 102. A force sensor output signal corresponding to the I.V. solution pressure may be used to calculate, for example, I.V. solution flow rates or check for occlusions in the I.V. solution flow path. A variety of well known distribution systems, such as peristaltic pumps and syringe pumps, utilize force sensor acquired information to control and monitor the infusion of I.V. solutions. However, when used in pressure measuring applications, force sensor 106 is generally expensive and/or suffers from long term stability problems.
FIG. 2, labeled prior art, illustrates in a plan view another conventional approach ("bladder approach") to measuring I.V. solution pressure involving a bladder housing 200 ("bladder approach") having flexible bladder 212 placed in series with I.V. tubes 204 and 208. In the bladder approach, bladder housing end 202 connects to an I.V. tube 204 which is connected to a solution source (not shown), and bladder housing end 206 connects to an I.V. tube 208 which is connected to a solution destination (not shown). The bladder housing 200 includes flexible pumping bladders 210 and 214. Bladders 210, 212, and 214 fill with I.V. solution as I.V. solution is pumped through the bladder housing 200.
Referring to FIG. 3, labeled prior art, in cross-section bladder housing 200 is illustrated having end regions positioned between solid surface 302, which is part of a pump housing, and pressure sensor 304. During operation, I.V. solution fills the interior of bladder housing 200, and pump piston 312 impinges upon bladder 212. Bladder 212, containing I.V. solution 314, transfers the pressure of the I.V. solution 314 to pressure sensor 304 through flexible bladder underside 316, protective membrane 308, and gel 310. Pressure sensor 304 typically employs a piezoresistive silicon pressure sensor 306 which provides high reliability at a low cost. However, to ensure sterility of the I.V. solution transported through bladder housing 200, the tubing 204 and 208 and bladder housing 200 must be disposable and periodically replaced which increase& the operating cost of the bladder approach. Additionally, the bladder approach requires a bladder housing 200 separate from the force sensor.